Noncontact Self-Vibration Compensated Position Sensitive Detector Based Low-Frequency Vibration Measurement

Vibration measurement is thought to be the most effective method to determine the health of a machine. This article presents the development of a real-time triangulation-based, noncontact vibration measuring system for the frequency range from 1 to 600 Hz. The primary objective of the measurement system is to measure low-frequency vibrations as low as 1 Hz using position sensitive detector (PSD), which overcomes the limitations of conventional PSD-based noncontact vibration measurement. A micro-electromechanical system (MEMS) digital accelerometer-based self-vibration compensation technique is incorporated into the system, which helps to track and nullify the undesired movements on the PSD platform. The measuring system is constructed using a National Instruments (NI) CompactRIO (cRIO) 9074 controller. This controller is built with an field programmable gate array (FPGA) and a real-time processor, which enables it to be entirely digitalized, stand-alone, and reconfigurable. The measurements of the displacement signals from PSD and Brüel & Kjær (B&K) accelerometer are compared for verification in the first stage of calibration, and the accuracy level was found to be high for frequencies ranging from 5 to 600 Hz. However, below 5 Hz, B&K shows higher error in the displacement data. The linear piezo positioning system (i.e., piezo stage) is then used to overcome this limitation and calibrate the low-frequency vibration amplitude below 5 Hz. The designed measurement system shows a good agreement with the displacement result obtained from the piezo stage for the measurement of vibration amplitude accurately between 1 and 75 Hz.